1. Technical Field of the Invention
The present invention relates to cellular telephone networks and, in particular, to cellular telephone networks supporting short message service message delivery.
2. Description of Related Art
Reference is now made to FIG. 1 wherein there is shown a block diagram of a conventional digital cellular telephone network 10. Many such networks 10 support a short message service (SMS) for use by subscribers in conjunction with the conventional cellular telephone service. The purpose of the short message service is to provide a means for transferring textual messages between short message entities (SMEs) 12 using the communications environment provided by the cellular telephone network 10.
The short message entities 12 participating in the short message service comprise short message terminals (SMT) 14 connected to the fixed telephone network 16 (comprising a public switched telephone network (PSTN) or other equivalent telephone network). The short message entities 12 further comprise the subscriber mobile stations (MS) 18 operating within the cellular telephone network 10. Short message service messages must originate with or terminate at one of the subscriber mobile stations 18.
A short message service center or message center (MC) 20 is connected to the fixed telephone network 16 and to the cellular telephone network 10. The message center 20 functions as a store and forward center for receiving and delivering short message service messages between the short message entities 12. In those instances where delivery of a short message service message to a short message service entity 12 fails, the message is stored in the message center 20, to be subsequently retrieved by the addressee short message entity at a later time.
The cellular telephone network 10 further includes a plurality of base stations 24 (only one shown) for effectuating radio frequency communications over an air interface 26 with the mobile stations 18. Each base station 24 is connected through a mobile switching center (MSC) 30 to the fixed telephone network 16. The mobile switching center 30 operates to control base station 24 operation, maintain a record (in its home location register 42 and visitor location register 44) of mobile station 18 operating parameters and location within the network 10 and switch, with the fixed telephone network 16, those cellular telephone calls originated by or terminated at the mobile stations 18. The mobile switching center 30 is further connected to the message center 20 used in providing short message services.
Delivery of a short message service message received from a short message service entity 12 to another short message service entity originates at the message center 20 wherein a short message service delivery point-to-point (SMSDPP) invoke communication is generated. The format 32 for the SMSDPP invoke communication is illustrated in FIG. 2, and includes a teleservice identifier 34 and bearer data 36. The format 32 of the SMSDPP invoke communication includes a number of other parameters 40 well known to those skilled in the art, but not specifically shown, including an identification of the addressor and addressee short message service entities 12 for the message. The teleservice identifier 34 identifies the teleservice (e.g., cellular messaging, cellular paging) to be used in delivering the message, as well as the type of air interface (e.g., time division multiple access (TDMA), or code division multiple access (CDMA)) 26 used in carrying the message. The bearer data 36 comprises the short message service message itself received from the addressor short message service entity 12), and is pre-formatted specifically to conform to the identified teleservice and air interface type that are believed by the message center 20 to be subsequently used in conveying the message to the addressee short message service entity 12.
With particular reference now to a short message service message addressed for delivery to a mobile station 18 as the addressee short message service entity 12, following generation of the SMSDPP invoke communication, the communication is transmitted from the message center 20 to the mobile switching center 30. At the mobile switching center 30, the addressee information is processed in the home location register 42 and perhaps the visitor location register 44 to determine routing information for the SMSDPP invoke communication to the addressee mobile station 18. Although not shown, the processing to determine the routing information may in fact occur in plural mobile switching centers 30 as the communication is relayed through the network 10 towards the addressee mobile station 18. In accordance with the determined routing information, the SMSDPP invoke communication is transmitted from the message center 20 to the base station 24 believed to be most proximate to the current location of the addressee mobile station 18. The communication is then delivered to the addressee mobile station 18 by means of a broadcast made over the air interface 26.
Delivery of the SMSDPP invoke communication including the short message service message fails if the addressee mobile station 18 is at the time of delivery operating over a type of air interface 26 different than the type of air interface specified in the teleservice identifier 34 of the SMSDPP invoke communication. The reason for this failure is that the bearer data 36 must be in the correct format in order to recover the transmitted short message service message. Typically, the bearer data is formatted to conform to the identified teleservice and air interface type assumed by the message center 20 to be used to convey the SMSDPP invoke communication. If the communication is instead transmitted over another type of air interface 26, the format of the bearer data does not match the air interface used, and the receiving mobile station 18 is unable to recover the transmitted short message service message from the bearer data.
Message delivery failure is particularly a problem in cellular networks 10 supporting the operation of mobile stations 18 with multi-mode capabilities and/or those networks that support the use of plural types of air interfaces 26. For example, a mobile station 18 may be selectively operable in multiple modes over both a TDMA air interface as well as a CDMA air interface. Similarly, the cellular network 10 may include base stations 24 operable in accordance with either or both a TDMA or CDMA communications protocol. At the point in time when the SMSDPP invoke communication is generated at the message center 20, the message center has no actual knowledge of the air interface type currently being used by the network 10 to communicate with the addressee mobile station 18. This information is maintained in the home location register 42 and/or visitor location register 44 of the mobile switching center(s) 30 within the network 10, but it is not communicated to the message center 20. Instead, the message center 20 assumes mobile station operation in accordance with one of the supported air interfaces and formats the bearer data according to that assumption. Upon receipt of the SMSDPP invoke communication, the mobile switching center 30 simply forwards the communication over the air interface 26 currently being used by the addressee mobile station 18 without giving any consideration as to whether the air interface type specified in the teleservice identifier 34 matches the type of air interface actually being used by the mobile station. No manipulation or reformatting of the communication is made by the mobile switching center 30. If the air interface 26 over which the SMSDPP invoke communication is transmitted does not match the air interface type specified in the teleservice identifier parameter 34, short message service message delivery fails because the bearer data cannot be recovered.
There is accordingly a need for an improved method of formatting short message service messages for delivery over those cellular telephone networks supporting the use of plural types of air interfaces. Such an improved formatting method should be capable of facilitating the delivery of the SMSDPP invoke communication independent of the type of air interface actually being used by the addressee mobile station.